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2009

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Articles 2731 - 2760 of 4158

Full-Text Articles in Engineering

Non-Collocation Problems In Dynamics And Control Of Mechanical Systems, Timothy M. Obrzut Jan 2009

Non-Collocation Problems In Dynamics And Control Of Mechanical Systems, Timothy M. Obrzut

ETD Archive

Characteristics of mechanical systems with non-collocated sensors and actuators are investigated. Transfer function zeros location as a function of sensor position, zero-pole interlacing, and re-location of zeros are discussed in a context of presented examples. Some of the presented examples involving non-collocation are supported by experimental data. A case study involving a high speed machining spindle is examined. The control problems associated with non-collocation are studied along with the methods to solve them

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Smart Rotating Machines For Structural Health Monitoring, Dmitry Leonidovich Storozhev Jan 2009

Smart Rotating Machines For Structural Health Monitoring, Dmitry Leonidovich Storozhev

ETD Archive

The objective of this thesis is to explore an innovative approach to the on-line health monitoring of rotating machinery in the presence of structural damage using active magnetic bearings (AMBs). First, the detailed model of the rotor with the breathing transverse crack is developed using finite element method. Next, the experimental data from the rotating magnetically levitated healthy and cracked shafts, under specially designed external excitation force, was collected, analyzed and compared with the computer simulation. The obtained results demonstrate that the presented on-line health monitoring technique is very effective for detection of the structural damage in rotating machinery, and …

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Biogeography-Based Optimization: Synergies With Evolutionary Strategies, Immigration Refusal, And Kalman Filters, Dawei Du Jan 2009

Biogeography-Based Optimization: Synergies With Evolutionary Strategies, Immigration Refusal, And Kalman Filters, Dawei Du

ETD Archive

Biogeography-based optimization (BBO) is a recently developed heuristic algorithm which has shown impressive performance on many well known benchmarks. The aim of this thesis is to modify BBO in different ways. First, in order to improve BBO, this thesis incorporates distinctive techniques from other successful heuristic algorithms into BBO. The techniques from evolutionary strategy (ES) are used for BBO modification. Second, the traveling salesman problem (TSP) is a widely used benchmark in heuristic algorithms, and it is considered as a standard benchmark in heuristic computations. Therefore the main task in this part of the thesis is to modify BBO to …

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Slurry Based Coatings On Silicon Based Ceramics, Muralidhar Challarapu Jan 2009

Slurry Based Coatings On Silicon Based Ceramics, Muralidhar Challarapu

ETD Archive

Silicon carbide/silicon carbide (SiC/SiC) composites are the leading candidates for advanced high temperature structural components in gas turbine engine application. When SiC surface reacts with O2, protective SiO2 scales are formed, which are the basis for the corrosion resistance of SiC. Their main draw back in terms of usage in a gas-turbine engine is the volatilization of the protective silica scale because of the water vapor which is a byproduct of fuel combustion. The purpose of this project was to develop environmental barrier coatings (EBCs) based on ceramic powders to provide resistance to such moisture damage. In this thesis slurry-coating …

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Experimental Study Of Multirate Margin In Software Defined Multirate Radio, Tianning Shen Jan 2009

Experimental Study Of Multirate Margin In Software Defined Multirate Radio, Tianning Shen

ETD Archive

Due to the recent development of spectrally-efficient modulation schemes, IEEE 802.11 Wifi and IEEE 802.16 WiMax radios support wireless communication at multiple bit rates. While high-rate transmission allows delivering more information in less time, the corresponding performance improvement is less than expected due to the PHY- and MAC-layer overheads, imposed by the 802.11/16 standards. This is particularly true in wireless ad hoc networks as there exist rate-distance and rate-hop count tradeoffs. The concept of multi-rate margin is proposed in this thesis, which exploits the difference in communication characteristics at different rates and serves as the fundamental ingredient for an opportunistic …

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Multihop Transmission Opportunistic Protocol On Software Radio, Sachin C. Hirve Jan 2009

Multihop Transmission Opportunistic Protocol On Software Radio, Sachin C. Hirve

ETD Archive

The need of high speed communication motivates us to use high bit rate communication to transmit more information in as little time as possible. However, MAC layer protocol overheads dominate the transmission capability particularly at high rates and hinder high speed transmission. Opportunistic transmission has been proposed to help to overcome this disadvantage by transmitting packets back-to-back without inter-packet delays. Though this approach alleviates the problem in single-hop wireless LAN scenario, it doesn't help in multi-hop networks. This thesis presents an approach for multi-hop wireless networks, which is named as Multi-hop Transmission OPportunity (MTOP). It achieves better performance by ensuring …

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Performance Engineering Of A Lightweight Fault Tolerance Framework, Hua Chai Jan 2009

Performance Engineering Of A Lightweight Fault Tolerance Framework, Hua Chai

ETD Archive

It is well-known that the Paxos algorithm can be used to build provably correct practical fault tolerant systems. In this thesis, a lightweight consensus framework - Paxos-Based Fault Tolerance (PFT) framework and its practical implementation is presented. It also includes how the system tolerates faults under practical conditions where the replicas might not be strictly homogeneous due to the asynchrony of their deployment environment. A comprehensive performance evaluation study is performed on the PFT framework. The approaches that can optimize the fault tolerance mechanisms under various practical scenarios are also discussed

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On Traffic Analysis Attacks To Encrypted Voip Calls, Yuanchao Lu Jan 2009

On Traffic Analysis Attacks To Encrypted Voip Calls, Yuanchao Lu

ETD Archive

The increasing popularity of VoIP telephony has brought a lot of attention and concern over security and privacy issues of VoIP communication. This thesis proposes a new class of traffic analysis attacks to encrypted VoIP calls. The goal of these attacks is to detect speaker or speech of encrypted VoIP calls. The proposed traffic analysis attacks exploit silent suppression, an essential feature of VoIP telephony. These attacks are based on application-level features so that the attacks can detect the same speech or the same speaker of different VoIP calls made with different VoIP codecs. We evaluate the proposed attacks by …

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Tracking In Wireless Sensor Network Using Blind Source Separation Algorithms, Anil Babu Vikram Jan 2009

Tracking In Wireless Sensor Network Using Blind Source Separation Algorithms, Anil Babu Vikram

ETD Archive

This thesis describes an approach to track multiple targets using wireless sensor networks. In most of previously proposed approaches, tracking algorithms have access to the signal from individual target for tracking by assuming (a) there is only one target in a field, (b) signals from different targets can be differentiated, or (c) interference caused by signals from other targets is negligible because of attenuation. We propose a general tracking approach based on blind source separation, a statistical signal processing technique widely used to recover individual signals from mixtures of signals. By applying blind source separation algorithms to mixture signals collected …

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Flow Measurements In Turbulent Flow Fields With Magnetic Resonance Phase Velocity Mapping, Navneeth Sagar Reddy Lakkadi Jan 2009

Flow Measurements In Turbulent Flow Fields With Magnetic Resonance Phase Velocity Mapping, Navneeth Sagar Reddy Lakkadi

ETD Archive

Arterial stenosis (narrowing) is due to vascular disease that, if untreated, leads to death. The stenosis causes the development of complex flow which results in high energy losses and great forces between blood and tissue. Traditionally, turbulent flows lead to signal loss in magnetic resonance (MR) image acquisitions, resulting in loss of diagnostic information. With the advancement in MR hardware and software, some of the limitations of MR in turbulent flow fields may have been reduced or eliminated. This study evaluated the potential of MR phase velocity mapping (MRPVM), a clinical velocimetry technique, under turbulent flow conditions such as those …

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Modeling And Feedback Control Of A Mems Electrostatic Actuator, Jason Edwards Jan 2009

Modeling And Feedback Control Of A Mems Electrostatic Actuator, Jason Edwards

ETD Archive

This thesis describes the mathematical modeling and closed-loop voltage control of a MEMS electrostatic actuator. The control goal is to extend the travel range of the actuator beyond the open-loop pull-in limit of one third of the initial gap. Three controller designs are presented to reach the control goal. The first controller design utilizes a regular fourth order Active Disturbance Rejection Controller (ADRC) and is able to achieve 97 of the maximum travel range. The second design also uses a fourth order ADRC, while additional modeling information is included in an Extended State Observer (ESO), which is part of the …

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Load Frequency Control Of Multiple-Area Power Systems, Yao Zhang Jan 2009

Load Frequency Control Of Multiple-Area Power Systems, Yao Zhang

ETD Archive

In an interconnected power system, as a power load demand varies randomly, both area frequency and tie-line power interchange also vary. The objectives of load frequency control (LFC) are to minimize the transient deviations in theses variables (area frequency and tie-line power interchange) and to ensure their steady state errors to be zeros. When dealing with the LFC problem of power systems, unexpected external disturbances, parameter uncertainties and the model uncertainties of the power system pose big challenges for controller design. Active disturbance rejection control (ADRC), as an increasingly popular practical control technique, has the advantages of requiring little information …

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A Frequency Response Based Approach To Dc-Dc Control Loop Design, Jack Andrew Redilla Jan 2009

A Frequency Response Based Approach To Dc-Dc Control Loop Design, Jack Andrew Redilla

ETD Archive

This thesis encompasses control theory, mathematical models and practical methods for developing high performance control loops for compact DC-DC power converters. In this research we compare an existing hardware control loop design developed through traditional empirical tuning methods to a control loop established by a proposed systematic design approach. To address the many problems of ad-hoc controller design for DC-DC converters, we develop a procedure utilizing tools from frequency domain analysis and loop shaping techniques. This design approach is used to ensure control loop stability and to verify improved loop performance. This systematic control loop design procedure can be utilized …

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Structural And Thermal Analysis Of Flange For Lng Applications, Mayank D. Kalbhor Jan 2009

Structural And Thermal Analysis Of Flange For Lng Applications, Mayank D. Kalbhor

ETD Archive

Structural and thermal analysis of the flange used in connection with hose for the transportation of LNG was computationally simulated by the method of finite element and probabilistically evaluated in view of the several uncertainties in the performance parameters. The distribution function and sensitivity factors for the maximum stresses were found out. The effect of various random variables including geometry, structural/thermal properties etc on the maximum stresses were studied probabilistically. These results were useful to identify the most critical random variable in order to optimize the design well before it is introduced in the market. This reduces the manufacturing cost …

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Structural And Thermal Analysis Of Hose For Lng Applications, Bipin G. Kashid Jan 2009

Structural And Thermal Analysis Of Hose For Lng Applications, Bipin G. Kashid

ETD Archive

Finite element analysis (FEA) of the hose assembly used for transportation of Liquefied natural gas (LNG) has become a powerful tool in predicting the deformation and stress distributions. FEA helps in analyzing the model and optimizing the design in hostile environment. In the present work, computations are made to predict the maximum stresses caused due to structural and thermal effects in the LNG transportation. The analysis leads to the selection of the appropriate materials to be used and to the identification of both the most critical measurements and parameters. Most engineering design methods are deterministic, but in reality, many engineering …

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Heat Transfer In Electroosmotic Flow Of Power-Law Fluids In Micro-Channel, Omkareshwar Rao Bakaraju Jan 2009

Heat Transfer In Electroosmotic Flow Of Power-Law Fluids In Micro-Channel, Omkareshwar Rao Bakaraju

ETD Archive

The present study examines heat transfer in electro-osmotic flow of power-law fluids in a micro-channel analytically. The boundary layer equations governing the flow of power-law fluids in a micro-channel have been solved. Heat transfer characteristics such as the temperature distribution and Nusselt number are presented for parametric values of electro-kinetic parameter kH(where k-1 is the Debye length and H is semi-channel height of the micro-channel) and Brinkman number. Uniform surface heat flux boundary condition has been considered. The effects of the Brinkman number on the Nusselt number for specific values of the flow behavior index (n) are analytically determined. This …

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Tomato Bushy Stunt Virus (Tbsv), A Versatile Platform For Polyvalent Display Of Antigenic Epitopes And Vaccine Design, Shantanu Kumar, Wendy Ochoa, Pratik Singh, Catherine Hsu, Anette Schneemann, Marianne Manchester, Mark Olson, Vijay Reddy Jan 2009

Tomato Bushy Stunt Virus (Tbsv), A Versatile Platform For Polyvalent Display Of Antigenic Epitopes And Vaccine Design, Shantanu Kumar, Wendy Ochoa, Pratik Singh, Catherine Hsu, Anette Schneemann, Marianne Manchester, Mark Olson, Vijay Reddy

United States Army: Publications

Viruses-like particles (VLPs) are frequently being used as platforms for polyvalent display of foreign epitopes of interest on their capsid surface to improve their presentation enhancing the antigenicity and host immune response. In the present study, we used the VLPs of Tomato bushy stunt virus (TBSV), an icosahedral plant virus, as a platform to display 180 copies of 16 amino acid epitopes of ricin toxin fused to the C-terminal end of a modified TBSV capsid protein (NΔ52). Expression of the chimeric recombinant protein in insect cells resulted in spontaneous assembly of VLPs displaying the ricin epitope. Cryo-electron microscopy and image …

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Simulated Rainfall-Driven Dissolution Of Tnt, Tritonal, Comp B And Octol Particles, Susan Taylor, James H. Lever, Jennifer Fadden, Nancy Perron, Bonnie Packer Jan 2009

Simulated Rainfall-Driven Dissolution Of Tnt, Tritonal, Comp B And Octol Particles, Susan Taylor, James H. Lever, Jennifer Fadden, Nancy Perron, Bonnie Packer

United States Army: Publications

Live-fire military training can deposit millimeter-sized particles of high explosives (HE) on surface soils when rounds do not explode as intended. Rainfall-driven dissolution of the particles then begins a process whereby aqueous HE solutions can enter the soil and groundwater as contaminants. We dripped water onto individual particles of TNT, Tritonal, Comp B and Octol to simulate how surface-deposited HE particles might dissolve under the action of rainfall and to use the data to verify a model that predicts HE dissolution as a function of particle size, particle composition and rainfall rate. Particle masses ranged from 1.1 to 17 mg …

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Complementary And Alternative Medicine For The Allergist-Immunologist: Where Do I Start?, Renata J. M. Engler, Catherine M. With, Philip J. Gregory, Jeff M. Jellin Jan 2009

Complementary And Alternative Medicine For The Allergist-Immunologist: Where Do I Start?, Renata J. M. Engler, Catherine M. With, Philip J. Gregory, Jeff M. Jellin

United States Army: Publications

Complementary and alternative medicine (CAM) therapies present a growing information management challenge for physicians because nearly 40% of their patients may be using and another 50% may be considering use of CAM as part of their health care regimen. The National Health Statistics Reports for 2007 described the most commonly used nonvitamin, nonmineral therapy as natural products (eg, herbals at 17.7%). More than5% of children under the age of 18 years used CAM for allergic conditions including asthma. The amount and quality of information available and concerns about liability risk represent a challenge for most physicians. This review focuses on …

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First Results From Radar Profiles Collected Along The Us-Itase Traverse From Taylor Dome To South Pole (2006–2008), Brian C. Welch, Robert W. Jacobel, Steven A. Arcone Jan 2009

First Results From Radar Profiles Collected Along The Us-Itase Traverse From Taylor Dome To South Pole (2006–2008), Brian C. Welch, Robert W. Jacobel, Steven A. Arcone

United States Army: Publications

The 2006/07 and 2007/08 US-ITASE traverses from Taylor Dome to South Pole in East Antarctica provided opportunities to survey the subglacial and englacial environments using 3MHz and 200MHz radar. We present first results of these new ground-based radar data. A prominent basal deformation layer indicates different ice-flow regimes for the northern and southern halves of the Byrd Glacier drainage. Buried dune stratigraphy that appears to be related to the megadunes towards the west occurs at depths of up to 1500 m. At least two new water-filled subglacial lakes were discovered, while two recently drained lakes identified from repeat ICESat surface …

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Selecting And Conserving Lands For Biodiversity: The Role Of Remote Sensing, John Wiens, Robert Sutter, Mark Anderson, Jon Blanchard, Analie Barnett, Naikoa Aguilar-Amuchastegui, Chadwick Avery, Stephen Laine Jan 2009

Selecting And Conserving Lands For Biodiversity: The Role Of Remote Sensing, John Wiens, Robert Sutter, Mark Anderson, Jon Blanchard, Analie Barnett, Naikoa Aguilar-Amuchastegui, Chadwick Avery, Stephen Laine

United States Air Force: Publications

A major focus of conservation is on protecting areas to ensure the persistence of biological diversity. Because such areas may be large, not easily accessible, subject to change, and sensitive to the surrounding landscape, remote sensing can be a valuable tool in establishing and managing protected areas. We describe three case studies to illustrate how remote sensing can contribute to setting priorities for conservation actions, monitoring the status of conservation targets, and evaluating the effectiveness of conservation strategies. In the Connecticut River watershed, remote sensing has been used to assess flood regimes and identify key areas of floodplain forests and …

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Educating Engineers: A History Of Engineering Education At Valparaiso University, Edgar J. Luecke Jan 2009

Educating Engineers: A History Of Engineering Education At Valparaiso University, Edgar J. Luecke

Engineering Faculty Publications, Patents, Presentations

No abstract provided.

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One-Pot Synthesis Of Anionic (Nitrogen) And Cationic (Sulfur) Codoped High-Temperature Stable, Visible Light Active, Anatase Photocatalysts, Suresh Pillai, Declan Mccormack, Steven Hinder, Pradeepan Periyat Jan 2009

One-Pot Synthesis Of Anionic (Nitrogen) And Cationic (Sulfur) Codoped High-Temperature Stable, Visible Light Active, Anatase Photocatalysts, Suresh Pillai, Declan Mccormack, Steven Hinder, Pradeepan Periyat

Articles

No abstract provided.

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Surface-Initiated Titanium-Mediated Coordination Polymerization From Catalyst-Functionalized Single And Multiwalled Carbon Nanotubes, Dimitrios Priftis, Nikolaos Petzetakis, Georgios Sakellariou, Marinos Pitsikalis, Durairaj Baskaran, Jimmy W. Mays, Nikos Hadjichristidis Jan 2009

Surface-Initiated Titanium-Mediated Coordination Polymerization From Catalyst-Functionalized Single And Multiwalled Carbon Nanotubes, Dimitrios Priftis, Nikolaos Petzetakis, Georgios Sakellariou, Marinos Pitsikalis, Durairaj Baskaran, Jimmy W. Mays, Nikos Hadjichristidis

United States Department of Energy: Publications

Single (SWNTs) and multiwalled (MWNTs) carbon nanotubes were functionalized with a titanium alkoxide catalyst through a Diels-Alder cycloaddition reaction. The catalyst-functionalized carbon nanotubes (CNTs) were used for the surface initiated titanium-mediated coordination polymerizations of L-lactide (L-LA), ε-caprolactone (ε-CL) and n-hexyl isocyanate (HIC) employing the “grafting from” technique. 1H NMR, IR and Raman spectra showed that the precursor catalyst was successfully synthesized and covalently attached on the CNTs surface. Thermogravimetric analysis (TGA) revealed that the grafted poly(L-lactide) (PLLA) content could be controlled with time. The final polymer-grafted CNTs were readily dissolved in organic solvents as compared to the insoluble pristine …

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Morphology And Deformation Mechanisms And Tensile Properties Of Tetrafunctional Multigraft Copolymers, Yongxin Duan, Mahendra Thunga, Ralf Schlegel, Konrad Schneider, Erik Rettler, Roland Weidisch, Heinz W. Siesler, Manfred Stamm, Jimmy W. Mays, Nikos Hadjichristidis Jan 2009

Morphology And Deformation Mechanisms And Tensile Properties Of Tetrafunctional Multigraft Copolymers, Yongxin Duan, Mahendra Thunga, Ralf Schlegel, Konrad Schneider, Erik Rettler, Roland Weidisch, Heinz W. Siesler, Manfred Stamm, Jimmy W. Mays, Nikos Hadjichristidis

United States Department of Energy: Publications

Morphology and deformation mechanisms and tensile properties of tetrafunctional multigraft (MG) polystrene-g-polyisoprene (PS-g-PI) copolymers were investigated dependent on PS volume fraction and number of branch points. The combination of various methods such as TEM, real time synchrotron SAXS, rheo-optical FTIR, and tensile tests provides comprehensive information at different dimension levels.TEMand SAXS studies revealed that the number of branch points has no obvious influence on the microphase-separated morphology of tetrafunction MG copolymers with 16 wt % PS. But for tetrafunctional MG copolymers with 25 wt % PS, the size and integrity of PS microdomains decrease with increasing number of branch point. …

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High-Pressure Micellar Solutions Of Polystyrene-Block-Polybutadiene And Polystyrene-Block-Polyisoprene In Propane Exhibit Cloud-Pressure Reduction And Distinct Micellization End Points, Winoto Winoto, Sugata P. Tan, Youqing Shen, Maciej Radosz, Kunlun Hong, Jimmy W. Mays Jan 2009

High-Pressure Micellar Solutions Of Polystyrene-Block-Polybutadiene And Polystyrene-Block-Polyisoprene In Propane Exhibit Cloud-Pressure Reduction And Distinct Micellization End Points, Winoto Winoto, Sugata P. Tan, Youqing Shen, Maciej Radosz, Kunlun Hong, Jimmy W. Mays

United States Department of Energy: Publications

Micellar solutions of polystyrene-block-polybutadiene and polystyrene-block-polyisoprene in propane are found to exhibit significantly lower cloud pressures than the corresponding hypothetical nonmicellar solutions. Such a cloud-pressure reduction indicates the extent to which micelle formation enhances the apparent diblock solubility in near-critical and hence compressible propane. Concentration-dependent pressure-temperature points beyond which no micelles can be formed, referred to as the micellization end points, are found to depend on the block type, size, and ratio. The cloud-pressure reduction and the micellization end point measured for styrene-diene diblocks in propane should be characteristic of all amphiphilic diblock copolymer solutions that form micelles in compressible …

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Feasibility, Economics, And Environmental Impact Of Producing 90 Billion Gallons Of Ethanol Per Year By 2030, Todd West, Katherine Dunphy-Guzman, Amy Sun, Len Malczunski, David Reichmuth, Richard Larson, James Ellison, Robert Taylor, Vincent Tidwell, Lennie Klebanoff, Patricia Hough, Andrew Lutz, Christopher Shaddix, Norman Brinkman, Candace Wheeler, David O'Toole Jan 2009

Feasibility, Economics, And Environmental Impact Of Producing 90 Billion Gallons Of Ethanol Per Year By 2030, Todd West, Katherine Dunphy-Guzman, Amy Sun, Len Malczunski, David Reichmuth, Richard Larson, James Ellison, Robert Taylor, Vincent Tidwell, Lennie Klebanoff, Patricia Hough, Andrew Lutz, Christopher Shaddix, Norman Brinkman, Candace Wheeler, David O'Toole

United States Department of Energy: Publications

This paper addresses a national interest in investigating the potential of displacing a large fraction of U.S. gasoline use by 2030 with ethanol. This study assesses the feasibility, implications, limitations, and enablers of producing 90 billion gallons ethanol per year by 2030. We developed a dynamic supply chain model, the Biofuels Deployment Model (BDM), and conducted sensitivity analyses to determine the parameters that most affect the feasibility, cost-competitiveness, and greenhouse gas impact of large-scale ethanol production. Though we found no theoretical barriers to achieving the stated goal, we identified a number of practical obstacles that need to be addressed. In …

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Biomineralization Associated With Microbial Reduction Of Fe3+ And Oxidation Of Fe2+ In Solid Minerals, Gengxin Zhang, Hailiang Dong, Hongchen Jiang, Ravi K. Kukkadapu, Jinwook Kim, Dennis Eberl, Zhiqin Xu Jan 2009

Biomineralization Associated With Microbial Reduction Of Fe3+ And Oxidation Of Fe2+ In Solid Minerals, Gengxin Zhang, Hailiang Dong, Hongchen Jiang, Ravi K. Kukkadapu, Jinwook Kim, Dennis Eberl, Zhiqin Xu

United States Department of Energy: Publications

Iron-reducing and oxidizing microorganisms gain energy through reduction or oxidation of iron, and by doing so play an important role in the geochemical cycling of iron. This study was undertaken to investigate mineral transformations associated with microbial reduction of Fe3+ and oxidation of Fe2+ in solid minerals. A fluid sample from the 2450 m depth of the Chinese Continental Scientific Drilling project was collected, and Fe3+-reducing and Fe2+-oxidizing microorganisms were enriched. The enrichment cultures displayed reduction of Fe3+ in nontronite and ferric citrate, and oxidation of Fe2+ in vivianite, siderite, and monosulfide …

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Uranium Extraction From Laboratory-Synthesized, Uranium-Doped Hydrous Ferric Oxides, Steven Smith, Matthew Douglas, Dean A. Moore, Ravi K. Kukkadapu, Bruce Arey Jan 2009

Uranium Extraction From Laboratory-Synthesized, Uranium-Doped Hydrous Ferric Oxides, Steven Smith, Matthew Douglas, Dean A. Moore, Ravi K. Kukkadapu, Bruce Arey

United States Department of Energy: Publications

The extractability of uranium (U) from synthetic uranium-hydrous ferric oxide (HFO) coprecipitates has been shown to decrease as a function of mineral ripening, consistent with the hypothesis that the ripening process will decrease uranium lability. To evaluate this process, three HFO suspensions were coprecipitated with uranyl (UO22+) and maintained at pH 7.0 ± 0.1. Uranyl was added to the HFO post-precipitation in a fourth suspension. Two suspensions also contained either coprecipitated silicate(Si-U-HFO) or phosphate (P-U-HFO).After precipitation of the HFOs, at time intervals of 1 week, 1 month, 6 months, 1 year, and 2 years, aliquots of each …

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Reduction And Long-Term Immobilization Of Technetium By Fe(Ii) Associated With Clay Mineral Nontronite, Deb Jaisi, Hailiang Dong, Andrew Plymale, James K. Fredrickson, John M. Zachara, Steve Heald, Chongxuan Liu Jan 2009

Reduction And Long-Term Immobilization Of Technetium By Fe(Ii) Associated With Clay Mineral Nontronite, Deb Jaisi, Hailiang Dong, Andrew Plymale, James K. Fredrickson, John M. Zachara, Steve Heald, Chongxuan Liu

United States Department of Energy: Publications

99Tc is formed mostly during nuclear reactions and is released into the environment during weapons testing and inadvertent waste disposal. The long half-life, high environmental mobility (as Tc(VII)O4−) and its possible uptake into the food chain cause 99Tc to be a significant environmental contaminant. In this study, we evaluated the role of Fe(II) in biologically reduced clay mineral, nontronite (NAu-2), in reducing Tc(VII) O4− to poorly soluble Tc(IV) species as a function of pH and Fe(II) concentration. The rate of Tc(VII) reduction by Fe(II) in NAu-2 was higher at neutral pH (pH 7.0) …

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